In a continuously variable transmission for use in automotive vehicles (see, for example, Japanese Unexamined Utility Model Publication No. H3-84459) for example, a pair of conical pulleys (sheaves) 51, 52 are mounted to a driving shaft 50 shown in FIG. 10. One 51 of the conical pulleys is capable of being axially moved by a cylinder piston unit 53. The width of a groove defined between the conical pulley pair 51, 52 may be increased or decreased by such a movement of the pulley. A belt-like power transmission chain 56 is entrained between the conical pulley pair 51, 52. The groove width is increased or decreased whereby the power transmission chain 56 is moved toward the center of the conical pulleys 51, 52 or pushed toward outer sides of the pulleys, as making sliding contact with conical surfaces 51a, 52a of the conical pulleys 51, 52.
The power transmission chain 56 is formed by bendably interconnecting unit members into an endless belt form by means of load pins 55 (pins for use in power transmission chain), the unit member having a structure wherein thin plates called link plates 54 are overlapped on one another. The load pin 55 is formed by machining opposite ends of a flat-plate member in conformity to the conical surfaces 51a, 52a of the pulleys 51, 52. The load pin is adapted to make contact with the conical surfaces 51a, 52a of the pulleys 51, 52 at the opposite end faces thereof when the power transmission chain 56 is entrained between the conical pulley pair 51, 52. The power transmission chain 56 is adapted to transmit power by way of frictional force based on the contact between the load pins and the conical surfaces.
All the load pins 55 must be finished in an exact length and must have the opposite end faces finished in predetermined configurations. Therefore, the load pin 55 is subjected to a grinding process using a grinding wheel. FIG. 11 schematically shows the locations of members involved in the grinding process. FIG. 11(a) is a plan view and FIG. 11(b) is a side view. The grinding process is performed as follows. First, a bundle of load pins 55 are retained on a support portion 58 by means of a jig 57. In this state, one end face of each load pin is ground by a grinding wheel 59. Subsequently, the bundle is turned over and the other end face of each load pin is ground.